不怎么 is a softer, more colloquial way of saying 'not very.' It's milder than 不太 (bù tài) and much milder than 不 alone. It's a polite way to express mild dissatisfaction or indifference.
grammar
不怎么 + adjective/verb: 不怎么好 (not very good), 不怎么去 (don't go much), 不怎么吃 (don't eat much of it).
